Continued.....
The old ELCB came in two types: Voltage-operated and current-operated. For economy, most residences using an ELCB used the voltage type.
With this system the main grounding lead didn't go directly to the rod, but through a solenoid coil in the ELCB. The characteristics were such that the breaker would trip before the potential on the ground wiring of the house could exceed 40 to 50 volts. Voltage ELCBs were installed up until about the early 1970s. They're now considered obsolete, but many are still in use.
The more sophisticated current-balance ELCB operates like the GFCI, but where used in the past they were normally quite low sensitivity types compared to today. For example, my 1966 edition of the IEE Regs. specifies that a sensitivity greater than 500mA is not considered necessary except in special circumstances. Anywhere which had such high ground resistance values that a 500mA ELCB wouldn't trip would most likely have been supplied by a PME system and therefore ELCBs wouldn't be necessary.
During the last 20 years or so, earth-leakage protection has gradually increased. The current-operated ELCB got renamed twice: First it became an RCCB (Residual Current Circuit Breaker) and quite recently it was changed to RCD (Residual Current Device).
Sensitivities increased to 100mA and it has become increasingly common for an ELCB/RCCB/RCD to be fitted even when not required by IEE Regs. (such as where PME is used). Some people now use a 30mA unit to protect the whole house.
As far as the "Regs." go (not actually a legal requirement for residential, remember, but usually followed) the current edition works around specified "disconnection" times for clearing a ground fault. These are 5 seconds for lights and other fixed appliances, and 0.4 sec. for outlets which may be used to feed handheld devices. If the loop impedance is too great for a normal fuse or C/B to clear an earth fault within these times then an RCD is required.
In practice, this still usually means that no RCD is needed on PME or older armor-earthed systems, but is where a ground-rod is used.
Although not necessary for compliance, the IEE now "suggests" that a 30mA RCD be used for all kitchen outlets, outdoor sockets, and other outlets "likely to be used to feed outdoor equipment" (e.g. hedge trimmers).
Bathrooms are considered a special case by the IEE. More on that next time.
Sorry to go on so long, but you did ask for details!
